The deposition behavior of particles during cold spraying is determined by plastic deformation of both substrate and impinging spray particles. In this paper, the in-situ heating and subsequent softening of the local substrate were examined to reveal their influence on the deposition behavior of spray particles and the microstructure and property of the cold-sprayed 316L stainless steel and copper coatings. Results show that the temperature of the substrate surface, where the spray gas stream and high velocity particles were projected on, increased to 300°C when the gas temperature was 500°C. Such effect is referred to as the in-situ substrate heating. The in-situ heating of the substrate surface was enhanced with the decrease in the gun nozzle traverse speed. With the decrease of nozzle traverse speed from 100 to 20 mm/s, the relative deposition efficiency significantly increased and the porosity of cold-sprayed 316L coatings decreased from 5.6% to 2.5%, and the micro-hardness of the coatings increased from 283 Hv to 351 Hv. The influence of the nozzle traverse speed on the microstructure and property of cold-sprayed coatings is discussed based on the influence of the in-situ heating and softening effect of substrate surface on its deformation behavior and particle deposition upon the impact of spray particles. The in-situ substrate surface heating is proposed as an essential processing parameter as a function of gun traverse speed during cold spraying.
Solution precursor plasma spraying (SPPS) was employed to prepare porous Sm0.5Sr0.5CoO3 (SSC) cathode for solid oxide fuel cell (SOFC). The surface and cross-sectional morphology of the SSC deposit were characterized by scanning electron microscopy. The effect of annealing on SSPS SSC microstructure was examined. The electrochemical behavior was investigated through the impedance spectroscopy. The results showed that the SPPS SSC cathode deposited at a spray distance of 80 mm exhibits multidimensional porous microstructure. The porous film of the partially crystalline perovskite phase with a fine microstructure was obtained after annealing at 900 °C for 2 hours in air. The electrochemical measurement showed that the specific surface resistance of SSC decreased significantly with the increase of test temperature and yielded a specific surface resistance of 2.6 Ω·cm2 at 800°C.
Thermally-sprayed LZ/YSZ double-layer coatings are promising candidate for the next generation thermal barrier coatings (TBCs) due to exceedingly low thermal conductivity and superior high-temperature phase stability. However, a delamination failure at LZ and YSZ interface were widely observed during TBCs service. Till today, the interfacial microstructure between LZ and YSZ remains unclear. In the present study, LZ splats were deposited on YSZ substrate to serve as a LZ/YSZ interface. The interfacial microstructure was explored by focused ion beam (FIB) and high-resolution transmission electron microscope (HR-TEM). The interfacial defects at splat interface were clearly observed and thoroughly discussed. These results would shed light on deeply understanding the interfacial failure of double-layer LZ/YSZ coatings.
The non-parabolic isothermal oxidation kinetics of low pressure plasma sprayed MCrAlY bond coat was investigated. To qualitatively explain the abnormal growth phenomenon of thermally grown oxides (TGO), the changes that occurred to their microstructure during the oxidation process were studied. Based on these observations, a modified model was developed to understand and quantitatively predict the non-parabolic oxidation and growth kinetics of TGO. This modified model, which fits well with experimental results, provides a novel method to quantitatively predict the long-term growth behaviour of TGO, and thereby benefits the development of long-life and highly reliable thermal barrier coatings.
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